The most glaring similarity is that their protagonists tend to be beta males, with some exceptions. As an American I find it refreshing. It is something American authors are usually bad at.

They both like to have a lot of dufus characters even though Moore mispells 'dufus'.

Now the contrast that justifies my neologism above. Their worlds are mirror images of each other. Pratchett places modern sensibilities in a fantasy world where Moore brings fantasy elements into ours.

"This is a bawdy tale. Herein you will find gratuitous shagging, murder, spanking, maiming, treason, and heretofore unexplored heights of vulgarity and profanity, as well as nontraditional grammar, split infinitives, and the odd wank . . . If that's the sort of thing you think you might enjoy, then you have happened upon the perfect story!"

Some are born great, some achieve greatness and some have greatness thrust upon them.

That's an interesting thought. I don't quite find the two to be that comparable. Although both Pterry (in DW anyway) and Moore are genre parodists, Moore's casts a little bit of a wider net. He started out more as a horror book/movie parodist (the vampire novels, the monsters attacking the little California town) and then stretched his literary wings to encompass a wider range of topics: ecology (Fluke), Shakespeare (Fool), impressionism (Sacre Blue) and even Christianity (Lamb, his best book). Many other authors tread the Moore path; parodies of all these genres as rampant. But Moore is a much better writer and, when he really wants to, unearths deep insights into this themes.

Pterry, on the other hand, was originally much more focused on becoming the Douglas Adams of fantasy, taking on the genre's ossified cliches and adding twists to them. His early work is completely derivative of Adams (down to the footnotes serving the same purpose as Adams Galactic Encyclopedia sidenotes). It took a while for Pterry to find his 'original' voice (many people say that "Mort" is the first truly great DW book; I would probably agree).

I don't know if I agree about the 'beta male' argument. Sam Vimes is no beta male. Neither is Wm. De Worde, Moist Von Lipwig, Lobsang or, in a quieter way until the end, Brutha. The only main beta male protagonist is Rincewind, for me Pterry's weakest character. But, like Moore, Pterry does feature some very strong alpa-females, like Susan, Granny and Nanny and, to a lesser degree, Polly. But nearly all of Moore's male characters (except, possibly, for the Fool in Fool and Biff in Lamb are beta males who tend to be drawn by their--er-petards by strong female characters.)

Between the two of them, I think that Pterry's best work is far more original than Moore's, as much as I love Moore. Pterry really did create a whole world and then upon it built a history, cultural heritage, geography, geology, and mythos that, at its best, deliver deep insights into the human condition. With the rare exception (Lamb), Moore's work doesn't generally extend far beyond parody.

I like Moore's books, but as Catch Up said, they are not as consistent. Sacre Blue took a bit of getting in to - a lot of background building and arty stuff before the proper story gets going . It's still good, but with a TP book I'm usually hooked within the first few pages.